The present invention is directed to a one-sided spot welding device and its method of use. More specifically, the present invention is directed to a one-sided spot welding device having an electromagnet to draw together and hold workpieces during a one-sided spot welding process.
Spot welding is a widely used and widely recognized technique for joining various metallic metal parts. More specifically, spot welding is a resistance welding technique that operates by applying welding current and clamping force to a small area (“spot”) of the parts to be welded. By so concentrating the welding current and force, heat generated by the welding current quickly melts the parts at the welding spot—rendering them joined upon removal of the welding current and a cooling of the parts.
Spot welding not only requires sufficient current to melt the materials to be joined, but also requires that sufficient pressure be exerted to maintain contact between the parts at the welding spot during the application of the welding current. To this end, various spot welding devices have been designed and used over the years. One common type of spot welding device is a multi-axis welding robot equipped with a spot welding gun, but other types also exist. A spot welding gun commonly comprises two gun arms between which the parts to be welded are clamped from opposite sides during welding. Clamping pressure is commonly provided by moving one or both the gun arms around a pivot axis by means of a pneumatic, electric or hydraulic cylinder. Electric current is passed from one gun arm weld electrode to the other—through the parts to be welded. Resistance to the transfer of electric current causes a buildup of heat, which temporarily melts the parts at the welding spot and leads to their joining.
Spot welding is widely used in the assembly of vehicles, such as automobiles. For example, spot welding is commonly employed to join various sections of an automobile body (e.g., side panels to a roof panel, etc.) In modern automobile construction, spot welding is also used to create “stack-ups” of sheet metal panels. Stack-ups are generally areas of body panels (e.g., door panels) where two or more pieces of sheet metal are stacked together and welded to produce reinforced areas in the resulting automobile body. The materials used in such stack-ups are often of dissimilar thickness and/or composition.
It can be readily understood by one skilled in the art that automobile bodies and other products that are manufactured using spot welding are often of complex shape. It can also be readily understood by one skilled in the art that the shape, size, and or orientation of certain components during manufacture can make it difficult if not impossible to properly locate a spot welding gun thereto. Further, the creation of stack-ups and other spot welding operations that require the insertion of a welding gun arm into the interior of a vehicle body or other structure also pose problems of access when using traditional spot welding techniques.
As a result of the foregoing problems, a considerable interest has developed in one-sided spot welding—that is, spot welding where the electric welding current is passed through the parts to be welded from only a single side. While the ability to perform one-sided spot welding is desirable, the ability to perform such welding has proven problematic.
One particular problem with one-sided spot welding relates to the difficulty in applying sufficient clamping force to the parts to be welded when welding from only one side. More specifically, the clamping force exerted on the parts to be welded during a one-sided spot welding process must generally be substantially commensurate with that of a common two-sided welding process in order to ensure proper part positioning and conductive contact. Consequently, with no gun arm or similar force-applying element pushing back from one side of the parts to be welded, providing an acceptable level of clamping force between a stack-up or other arrangement of parts to be welded can be difficult or impossible.
Therefore, an improved method of performing one-sided spot welding with the ability to adequately clamp together the parts to be welded is needed. The device and method of the present invention satisfies this need.